Today I came across this article on BBC News. In 1939 Tommy Godwin rode his bike for 75'065 miles. He continued into 1940 to complete the 100'000 miles.
To achieve this you have to ride more than 320 km daily. Tommy did this on a four gear bike, fixed problems himself and slept only a few hours the night. According to the article this is a world record that will most likely stand forever.